Difference between revisions of "Glycogen phosphorylase"

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An alternative rate equation without considering the allosteric regulation is given as <ref name="Lambeth_2002> Lambeth M.J. &  Kushmerick M.J. (2002). ''A computational model for glycogenolysis in skeletal muscle''. Ann Biomed Eng 30, 808–827</ref>
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An alternative rate equation without considering the allosteric regulation is given as <ref name="Lambeth_2002"> Lambeth M.J. &  Kushmerick M.J. (2002). ''A computational model for glycogenolysis in skeletal muscle''. Ann Biomed Eng 30, 808–827</ref>
  
 
<center><math> \frac{V_{maxf} \frac{Glycogen_{n+1} \times Pi}{K_{iGlyf} \times K_{Pi}} -\frac{V_{maxf} \times K_{Glyb} \times K_{iGlc1P}}{K_{iGlyf} \times K_{Pi} \times Keq} \times \frac{Glycogen_n \times Glc1P}{K_{Glyb} \times K_{iGlc1P}} }{1 + \frac{Glycogen_{n+1}}{K_{iGlyf}} + \frac{Pi}{K_{iPi}} + \frac{Glycogen_n}{K_{iGlyb}} + \frac{Glc1P}{K_{iGlc1P}} \frac{Glycogen_{n+1} \times Pi}{K_{Glyf} \times K_{iPi}} + \frac{Glycogen_n \times Glc1P}{K_{Glyb} \times K_{iGlc1P}} } </math></center>
 
<center><math> \frac{V_{maxf} \frac{Glycogen_{n+1} \times Pi}{K_{iGlyf} \times K_{Pi}} -\frac{V_{maxf} \times K_{Glyb} \times K_{iGlc1P}}{K_{iGlyf} \times K_{Pi} \times Keq} \times \frac{Glycogen_n \times Glc1P}{K_{Glyb} \times K_{iGlc1P}} }{1 + \frac{Glycogen_{n+1}}{K_{iGlyf}} + \frac{Pi}{K_{iPi}} + \frac{Glycogen_n}{K_{iGlyb}} + \frac{Glc1P}{K_{iGlc1P}} \frac{Glycogen_{n+1} \times Pi}{K_{Glyf} \times K_{iPi}} + \frac{Glycogen_n \times Glc1P}{K_{Glyb} \times K_{iGlc1P}} } </math></center>
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Revision as of 12:12, 1 April 2014

Glycogen phosphorylase (GP) is a dimeric enzyme that catalyses the reaction in which the terminal glucose residue from a glycogen chain is phosphorylated and cleaved from the chain, releasing it as Glc1P.

Chemical equation

Glycogen_{n+1} + Pi \rightleftharpoons Glycogen_{n} + Glc1P

Rate equation

MWC model was used to formualte the rate law. [1]

\frac{V_{max} \times n \times \frac{[Pi]}{K_{r,Pi}} \left( 1 + \frac{[Pi]}{K_{r,Pi}} + \frac{[Glc1P]}{K_{r,Glc1P}} \right)^{n-1} }{\left( 1 + \frac{[Pi]}{K_{r,Pi}} + \frac{[Glc1P]}{K_{r,Glc1P}} \right)^n + L_u \left( 1 + \frac{[Pi]}{K_{u,Pi}} + \frac{[Glc1P]}{K_{u,Glc1P}} \right)^n \left( \frac{1 + \frac{[Glc6P]}{K_{u,Glc6P}}}{1 + \frac{[AMP]}{K_{r,AMP}} + \frac{[Glc6P]}{K_{r,Glc6P}}} \right)^n } + \frac{V_{max} \times n \times \frac{[Pi]}{K_{r,Pi}} \left( 1 + \frac{[Pi]}{K_{r,Pi}} + \frac{[Glc1P]}{K_{r,Glc1P}} \right)^{n-1} }{\left( 1 + \frac{[Pi]}{K_{r,Pi}} + \frac{[Glc1P]}{K_{r,Glc1P}} \right)^n + L_t \left( 1 + \frac{[Pi]}{K_{t,Pi}} + \frac{[Glc1P]}{K_{t,Glc1P}} \right)^n \left( \frac{1 + \frac{[AMP]}{K_{t,AMP}} \frac{[Glc6P]}{K_{t,Glc6P}}}{1 + \frac{[AMP]}{K_{r,AMP}} + \frac{[Glc6P]}{K_{r,Glc6P}}} \right)^n \left( 1 + \frac{[ATP]}{K_{t,ATP}} \right)^n }




An alternative rate equation without considering the allosteric regulation is given as [2]

\frac{V_{maxf} \frac{Glycogen_{n+1} \times Pi}{K_{iGlyf} \times K_{Pi}} -\frac{V_{maxf} \times K_{Glyb} \times K_{iGlc1P}}{K_{iGlyf} \times K_{Pi} \times Keq} \times \frac{Glycogen_n \times Glc1P}{K_{Glyb} \times K_{iGlc1P}} }{1 + \frac{Glycogen_{n+1}}{K_{iGlyf}} + \frac{Pi}{K_{iPi}} + \frac{Glycogen_n}{K_{iGlyb}} + \frac{Glc1P}{K_{iGlc1P}} \frac{Glycogen_{n+1} \times Pi}{K_{Glyf} \times K_{iPi}} + \frac{Glycogen_n \times Glc1P}{K_{Glyb} \times K_{iGlc1P}} }

Parameter values

Parameter Value Units Organism Remarks
n 2 Dimensionless Recombinant, human muscle
V_{max} 50 \text{mM min}^{-1}
K_{r,Pi} 2.08 mM
K_{u,Pi} 4.32 mM
K_{t,Pi} 41.53 mM
K_{r, Glc1P} 0.67 mM
K_{u, Glc1P} 82.02 mM
K_{t, Glc1P} 27.92 mM
K_{r, AMP} 3.36 \times 10^{-3} mM
K_{t, AMP} 0.53 mM
K_{t, ATP} 3.9 mM
K_{r, Glc6P} 7.42 mM
K_{u, Glc6P} 0.56 mM
K_{t, Glc6P} 0.27 mM
L_{u} 5.93 Dimensionless
L_{t} 34741 Dimensionless

The parameter for the alternative equation are

Parameter Value Units Organism Remarks
V_{maxf} 50 [1] \text{mM min}^{-1} Rabbit
K_{iGlyf} 15[2] mM
K_{Pi} 4 [2] mM
K_{Glyb} 0.15 [2] mM
K_{iGlc1P} 10.1 [2] mM
K_{iPi} 4.6 [2] mM
K_{iGlyb} 4.4 [2] mM
K_{Glyf} 1.7 [2] mM
Keq 0.42 [2] mM

References

  1. ↑ 1.0 1.1 Palm, D.C. (2013). The regulatory design of glycogen metabolism in mammalian skeletal muscle (Ph.D.). University of Stellenbosch
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 Lambeth M.J. & Kushmerick M.J. (2002). A computational model for glycogenolysis in skeletal muscle. Ann Biomed Eng 30, 808–827
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